There are numerous circuits and other electronic devices that produce energy waves such as electromagnetic waves and microwaves. These circuits produce energy waves that are delivered to a destination through different wires, guides, and other mediums.
Energy waves can be difficult to control on various circuits, cables, wires, and other mediums that transport the energy waves because these mediums are “lossy.” Lossy materials and mediums lose energy by radiation, attenuation, or dissipation as heat. By being lossy, a portion of the signal is lost as is travels through the circuits, wires, and other mediums. Stated another way, a signal entering a lossy material will be greater at the point of entry than at the point of exit.
Microwave energy is particularly difficult to control as many of the materials and mediums that transport microwave energy are lossy. One exemplary circuit that generates and transports microwaves is a “monolithic microwave integrated circuit” or “MMIC.” Lost signal waves are unusable and decrease the efficiency of a MMIC as the signal strength decreases due to loss. Generally, the higher the frequency of the microwave, the more lossy the transmission medium and more inefficient the circuit. In certain applications, even signal losses that reduce the signal by small amounts, such as 1/10 of a decibel may result in a significant performance loss. One exemplary application where loss from energy waves such as microwaves is problematic is a power amplifier.
One structure used to reduce lossiness is a waveguide. Waveguides are structures that guide energy waves with minimal signal loss. Unfortunately, signal loss is still problematic with certain waves because the connection or interface between the circuit generating the energy waves and the waveguide can be lossy itself. This is especially an obstacle with a MMIC generating microwaves. Moreover, impedance miss-matches also cause signal losses. For example, the impedance of the MMIC, for example fifty ohms, may not match the impedance of the connected waveguide, for example two hundred and seventy ohms. In this example, an interface between the waveguide and MMIC attempts to match the fifty ohm impedance of the MMIC with the two hundred and seventy ohm impedance of the waveguide. These types of interfaces are known generally as “impedance matching interfaces” or “impedance matching and transforming interfaces.”
Besides impedance, circuits such as MMICS also have different modes of energy wave propagation compared to other energy transporting devices such as a waveguide. For example, a MMIC may have a mode of energy wave propagation of quasi-TEM (Transverse Electromagnetic) while a waveguide has a mode of energy wave propagation of TE10 (Transverse Electric, 10). These differing modes of energy wave propagation also contribute to loss in traditional interfaces. Impedance matching interfaces also match the differing modes of energy wave propagation to minimize loss.
Present interfaces between a MMIC and waveguide comprise numerous structures that include wirebonds, microstrips, pins, and other devices to connect a circuit to a waveguide or another structure. These interfaces also attempt to match and transform the impedance of the MMIC to the impedance at the waveguide. However, present impedance and mode of energy wave propagation matching interfaces between an integrated circuit such as a MMIC and a waveguide still have an unacceptable amount of loss.
Certain present impedance matching interfaces comprise devices with coaxial structures. Specifically, coaxial cable is used as an impedance matching interface depending on how it is used. Specifically, coaxial structures are utilized as impedance matching interfaces when their impedance is somewhere in between the impedance of the devices they are connecting. For example, a MMIC may have an impedance of fifty ohms and a waveguide may have an impedance of two hundred and seventy ohms. A coaxial structure may be used as part of the interface connecting the MMIC to the waveguide with an impedance of one hundred ohms. This impedance of one hundred ohms helps reduce loss of energy traveling from the fifty ohm MMIC to the two hundred and seventy ohm waveguide. Loss is reduced because the impedance of the devices transporting the energy changes much more gradually (fifty-hundred-two hundred and seventy) than merely connecting the MMIC to the waveguide (fifty-two hundred and seventy).
Despite their impedance matching abilities, many known impedance matching interfaces are complex as they comprise several different parts and require numerous mechanisms to be connected to circuits or other energy transmission devices. Further, known coaxial impedance matching interfaces are not used to directly connect an integrated circuit such as a MMIC to another energy transmission device such a waveguide.
One present interface that does minimize loss and accurately match impedance is described in commonly owned U.S. Pat. No. 7,625,131 issued on Dec. 1, 2009 entitled “Interface for Waveguide Pin Launch” wherein such patent is incorporated in its entirety, by reference. While this patent discloses an excellent interface, the interface does have several parts. Another present interface that reduces loss is disclosed in co-pending, commonly owned U.S. patent application Ser. No. 11/853,287 entitled “Low Loss Interface” which is also incorporated in its entirety by reference. This application also discloses an excellent impedance matching device, but this device too has numerous parts. It would be desirable to provide an impedance matching interface with a coaxial structure that directly connects a circuit such as a MMIC to a waveguide.
Therefore, it would be advantageous to provide a coaxial interface that directly connected an integrated circuit, such as a MMIC, to a waveguide, or other structure that reduces signal loss by matching the impedance. It would also be advantageous to produce a coaxial interface that reduced loss that was inexpensive and easy to manufacture, particularly one that was constructed from parts that were commercially available such a coaxial cable or other type of coaxial materials.